Correct - originally the system was just going against public opinion but with more and more stats over the years and tweaks there were other factors going on.
So while the original premise is correct and lots easier to explain there are some other things. For a long time this system did not actually start until teams had 4 games but then we (drinking gambling buddies) started to put some big restrictions on the difference between 2 teams and started with week 3 instead of 4.
N.O./ Dallas is a perfect example. If both teams had 4 games under their belts it would be a play.
"A" picks are all Home Favorites playing bad. Teams that are good but playing poorly AT HOME have a huge psychological boost and want to really show the home town fans they ARE good! Packers/Bears. Packers at home I would be betting the farm on the Packers!
BTW - I have an NBA system that is my real bread and butter and I HATE the NBA! It's all about numbers :-) It was a chase but won 64% last year in 170 games playing the final 2 or 3 games of a chase. Post #18 is where it gets a little more clear what I'm doing.